如何从mongoose模型中的另一个模型访问字段

const mongoose = require('mongoose');

const postSchema = new mongoose.Schema({
  title: String,
  content: String
});

const userSchema = new mongoose.Schema({
  name: String,
  posts: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Post' }]
});

const Post = mongoose.model('Post', postSchema);
const User = mongoose.model('User', userSchema);

const post1 = new Post({ title: 'Post 1', content: 'Content 1' });
const post2 = new Post({ title: 'Post 2', content: 'Content 2' });

const user = new User({ name: 'John', posts: [post1, post2] });

post1.save();
post2.save();
user.save();

User.findOne({ name: 'John' })
  .populate('posts')
  .exec((err, user) => {
    if (err) {
      console.error(err);
    } else {
      console.log(user.posts[0].title); // 输出：Post 1
      console.log(user.posts[0].content); // 输出：Content 1
    }
  });